1. Field of the Invention
The present invention relates to a high speed photographic device, a method for controlling a high speed photographic device, and a computer program; and more particularly, the present invention relates to an improvement of a high speed photographic device which is for photographing a photographic subject which periodically repeats high speed motion and for displaying in real time a photography image in synchronization with its motion cycle.
2. Description of the Related Art
A high speed photographic device is a device which can photograph a photographic subject in high speed and, for example, can photograph a photographic subject at a photographing frame rate of 60 to 32000 frames per second (fps). Generally, when a photographing frame rate is higher than a display frame rate, a photography image cannot be directly displayed in real time. Therefore, in this sort of high speed photographic device, there is adopted a method which is slow reproduction and live observation as a method for displaying a photographed photographic subject.
The slow reproduction is a method in which a photography image is once stored in a storage device as picture recording information, and then, the photography image is observed by being displayed at the display frame rate; and the slow reproduction is a picture recording and reproducing method which reproduces at a speed slower than actual motion. In the case of the slow reproduction, all the photography images can be observed without omission; however, the photographic subject cannot be observed in real time. Furthermore, if the photographing frame rate becomes higher, a reproduction time becomes extremely longer as compared with a photography time; and consequently, it becomes difficult to find a photography image to be intended.
On the other hand, the live observation is a method which displays at the display frame rate by thinning the photography image. In the case of the live observation, the photographic subject can be observed in real time; however, a photography image of the photographic subject displayed on a display is a motion state with skipping some parts; and consequently, it is difficult to observe in detail.
In such a high speed photographic device, there is a problem in that adjustment of photographing conditions is not easy. In other photographic device in which a photographic subject remains stationary, an adjustment such as focusing, exposure, and frame rates is made while confirming a photographic screen; however, in the case of the high speed photographic device, even when either the slow reproduction or the live observation is used, an adjustment of such photographing conditions is not easy. That is, if the slow reproduction is used when the photographing conditions are adjusted, adjustment of the photographing conditions and confirmation by the slow reproduction have to be alternately repeated; and consequently, adjustment work becomes complicated and it takes time. On the other hand, if the live observation is used, the adjustment and the observation can be performed at the same time; however, photography images with skipping some parts of the photographic subject which is in high speed motion are displayed on the display one after the other; and consequently, there is a problem in that it is difficult to perform the adjustment of the photographing conditions.
Consequently, as a method which facilitates adjustment of photographing conditions in a high speed photographic device, the following methods are conceivable. As a first method, it is conceivable that the adjustment of the photographing conditions is performed by making a photographic subject remain stationary. However, for example, if in the case of a high speed photographic device which monitors a production line, the production line cannot be stopped only for adjusting the photographing conditions thereof. Therefore, the photographing conditions have to be adjusted in a state where the photographic subject is in high speed motion.
As a second method, it is conceivable that a photography image which makes the photographic subject remain stationary in a pseudo manner is obtained and the adjustment of the photographing conditions is performed by performing synchronous photography in which a photographing frame rate is made to coincide with a motion cycle of the photographic subject. However, in this sort of high speed photographic device, high speed photography is intended; but synchronous photography is not intended; and therefore, the photographing frame rate cannot be finely adjusted and the synchronous photography corresponding to the motion cycle of the photographic subject cannot be performed. For example, user-selectable photographing frame rates are discrete values such as 60, 125, 250, 500, 1000, 2000, 4000, 8000, 16000, and 32000 fps; and since its option is small, it is not possible to photograph the photographic subject in synchronization with motion of a fan which rotates at 32 Hz, for example, and to perform focus adjustment.
As a third method, it is conceivable that a stroboscope (for example, Japanese Unexamined Patent Publication Nos. 6-160171 and 2003-84208) is used. The stroboscope is a device which makes a stroboscopic illuminator for illuminating a photographic subject emit light periodically, and is a device which enables synchronous photography by making a light emitting cycle of the stroboscopic illuminator coincide with a motion cycle of the photographic subject in the case where the photographic subject repeats periodic motion such as rotation and vibration. In other words, by using an exposure difference between when light is emitted and when light is not emitted, the photographic subject is made to remain stationary in a pseudo manner in a state where the stroboscopic illuminator emits light; and accordingly, it becomes possible to photograph a synchronous image in synchronization with the motion cycle of the photographic subject. However, in the case where the synchronous photography is performed using the stroboscope, even when the stroboscopic illuminator is not required as exposure conditions of a camera, the stroboscopic illuminator has to be used; and therefore, there is a problem in that it becomes difficult to downsize an imaging device.